This application claims the priority of German Application Nos. 100 18 798.6 filed Apr. 15, 2000 and 100 57 765.2 filed Nov. 22, 2000, which are incorporated herein by reference.
This invention relates to a latch needle, particularly for knitting machines and more particularly for circular knitting machines.
Latch needles are utilized, for example, in circular knitting machines. At one end the latch needles have a hook, adjoined by a latch which is pivotally supported in a sawslot of the latch needle. The latch is arranged in such a manner that in its closed state it lies at or on the end of the hook and closes the trapping space partially bounded by the hook. In its open state the latch is swung back to rest on its back and thus opens the trapping space. Such latch needles which are present in large numbers in knitting machines, are supported in needle beds in which, during operation of the knitting machine, they are rapidly reciprocated in their longitudinal direction. During this occurrence, the latches snap open and closed. For this purpose they have to move easily which, as a rule, requires a certain lateral play between the latch and the needle.
During the knitting operation the hook of the latch needle captures a thread while the needle executes its reverse stroke. A thread which is located behind the latch situated in its reverse state, lies on the upper side of the needle and first closes the latch. Upon further needle motion the thread slides off the hook resulting in the formation of a loop. The thread captured by the hook during this occurrence must be able to slide in the inner hook space and the trapping space must be closed by the latch. Only upon the successive movement of the needle in the opposite direction may the thread slide out of the inner hook space, opening the catch and the trapping space. If the latch is lifted from the hook earlier and thus the trapping space is opened and the thread moves out of the trapping space between the hook tip and the latch, loops will be dropped, resulting in a defective knit of unacceptable quality
Latch needles are also frequently used to produce dual-thread knits. To ensure that such knits have a uniform appearance, it is of the utmost importance that the threads do not switch their sequence in the trapping space of the latch needle. Dual-thread knits, so-called plated knit goods, are manufactured frequently with a combination of unlike threads, for example, a natural fiber yarn and an elastomer thread. In such a product the elastomer thread should, as a rule, be situated on that side of the product which is not visible (that is, on the reverse side of the item). Such a requirement is not fulfilled if the threads switch position. Such an occurrence results in an undesired pattern because, as a rule, the two threads have different shapes and/or color as well as other different properties.
Further, particularly monofilaments, such as elastomer threads are reacting very strongly to damages. Deep surface scratches must be definitely avoided, since even the slightest damage to the thread surface may lead to thread breakage.
Latch needles are known, for example, from German Patent No. 1,069,812. The latch needle has a pivotally supported latch, whose latch spoon (noucat) is provided with a groove for receiving the hook tip. The latch is linear along its inner contour which bounds the trapping space in the closed state of the latch and in the closed state the inner contour of the latch adjoins directly the hook tip.
Right-left circular knitting machines, that is, unifacial circular knitting machines have a sinker ring with hold-down sinkers instead of a dial. Such a ring or sinkers are needed to hold the knit product. For this purpose the sinkers, when the knitting machine needles are in their respective uppermost position, are moved past the loop forming portion of the needle and hold down the last-formed loop. During operation the knitting machine needles are exposed to a high degree of wear, for example, because of the high operating speed of the knitting machine, because of the yarns to be handled, or because of abrasive wear or other effects. The wear in most cases leads to an ever-increasing play in the latch bearing both in the axial and the radial direction resulting in lateral excursions of the latch during operation. The Coriolis force which is generated at the latches by the rotation of the cylinder of the knitting machine may amplify the lateral excursion of the latches of the knitting machine needles. If the lateral excursion of the latches is greater than the play between sinker and latch, the two frictionally engage one another, leading to lateral abrasions of the latch head.
Grooved needle latches as described in the above-noted German Patent No. 1,069,812 are particularly prone to such a wear which causes the originally rounded latch head to be transformed into a latch spoon having a groove with sharp edges. These may damage the threads which may lead to a rupture particularly of threads which break or tear relatively easily, such as elastomer threads.
German Offenlegungsschrift (application published without examination) No. 28 34 558 discloses a needle in which the needle hook is provided with a groove. Thus, the needle has a grooveless latch spoon and the latch head is configured such that it is accommodated by the deep groove in the needle hook when the latch is in its closed state. The inner contour of the closed trapping space, bounded by the hook and the latch, has at its transition from the latch to the hook a projection which prevents a thread motion within the inner space defined by the hook.
Such latch needles too, behave critically when simultaneously a plurality of threads are processed, such as, for example, during the manufacture of dual-thread knits.
British Published Patent Application No. 2,232,689 describes a latch needle for dual-thread knits. The latch needle has a pivotally supported latch which at its inner side is provided with a chamfer or step projecting into the inner space of the hook. The latch shank has a substantially constant height starting at the step and extending approximately to the rounded end of the latch shank. At its free end the latch has a latch spoon provided with a groove for receiving a portion of the hook tip. The step is configured as an oblique surface oriented in the direction of the hook tip and serves as a supporting surface for the threads of the dual-thread knit. The supporting surface is oriented toward the inner space of the hook and contacts the thread particularly when the threads lie on that border of the trapping space which is situated at the latch bearing.
During the knitting operation the threads are to be guided by the reciprocating motion of the needle from that end of the trapping space which is at the latch bearing into the inner space of the hook. Plating defects are intended to be avoided in such a needle structure as well.
It is an object of the invention to provide an improved latch needle of the above-outlined type which may be used in a diversified manner and which permits the manufacture of knit products having the desired quality.
This object and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the latch needle includes a shank; a hook formed at an end of the shank and having a hook tip; and a latch pivotally supported by the shank and cooperating with the hook. The latch has a closed state and a reverse state. In the closed state the hook and the latch together define a closed trapping space and in the reverse state the hook defines an open trapping space constituted essentially by an inner hook space. The latch includes an inner contour facing the trapping space in the closed state, a free end lying on the hook in the closed state and a stepped portion formed on the inner latch contour and adjoining the free latch end.
The latch needle according to the invention has a latch which, at its inner contour, that is, at that side which is oriented towards the trapping space, is provided with a stepped portion. Such a stepped portion, upon withdrawal of the needle, for example, upon knockover of a loop, guides the thread in the inner hook space in the direction of the needle back and thus away from the hook tip. The step guides the thread which is situated in the trapping space and from which a loop is formed during knockover, into the inner book space and prevents the thread from wedging between the hook tip and the latch spoon which would lead to an escape of the thread between the hook tip and the latch spoon. The stepped portion according to the invention effectively prevents dropped loops from occurring.
The above applies not only to mono-thread knits but in particular to dual-thread knits in which, for example, one thread having a relatively large diameter, such as a natural fiber thread and another thread, such as an elastomer thread having a relatively small diameter, are combined with one another. The invention ensures that the thin elastomer thread too, does not leave the trapping-space and thus does not form dropped loops.
Further, the thread is prevented from running against the hook tip and from being left suspended thereon. This advantageously reduces or avoids damages to the thread. In case of a dual-thread knit, the thread is prevented from remaining suspended on the hook tip and thus from being overtaken by the other thread. Plating defects are thus securely avoided or at least significantly reduced.
Further, the stepped portion on the inner contour of the needle latch according to the invention ensures that the two threads enter the inner hook space in their original sequence. The inner contour of the trapping space is relatively smooth so that neither of the threads remains suspended on an edge or a projection during the knitting process. This is particularly so because the stepped portion provided on the latch is oriented towards the hook tip and complements therewith a substantially smooth inner contour of the trapping spaces. The stepped portion and the adjoining region of the latch thus form an approximately bridge-like structure for guiding the thread into the inner hook space in the closed state of the latch, that is, when the latch spoon lies in the hook groove. In this manner a transition is formed substantially without interruption from the lower latch shaft edge (inner contour) to the lower edge of the hook tip and the adjoining inner edge, and thus neither a slip through (dropped loops) of the yam nor a switching of the yarn sequence way occur.
Such an effect is obtained particularly if the stepped portion is adjoining the hook tip in the closed position of the latch. In such a case the remaining intermediate space between the hook tip and the stepped portion may be particularly small. Preferably, such an intermediate, generally triangular space is open in the direction of the oppositely located inner wall of the trapping space or in the direction of the inner hook space. The stepped portion is preferably configured without an undercut to avoid intolerance between the hook tip and the latch as the latch opens and closes the thread space.
The stepped portion is preferably formed by a protuberance which projects into the trapping space as an imaginary prolongation of the inner arc of the hook. This arrangement prevents either loop drops or changes in the position of threads.
Preferably, the latch needle is of the type where a groove, providing for a nesting engagement between latch and hook, is formed in the hook. Such a groove is located in the vicinity of the hook tip. A latch needle with a grooved hook has, besides the above-discussed advantages, the further advantage that it is exposed to relatively slight wear. Particularly under the rigorous conditions of use in right-left circular knitting machines in which a lateral grinding of the latches may occur as discussed earlier in connection with German Patent No. 1,069,812, the latch needle having a grooved hook has significant advantages. The latch is at its free end laterally slightly flattened and is therefore narrower than the hook and, furthermore, has no groove. If, as the lateral latch play increases, and, as a result, the latch contacts the sinkers, such an event does not lead to a sharpening of the latch head as it is the case with grooved latches. Such an arrangement counteracts a potential damaging of the threads. Such a result is particularly advantageous when delicate threads such as elastomer threads or other monofilaments are used, because the slightest damage to the surface of such threads may lead to rupture. Therefore, this measure too, leads to an improvement of the quality of the knit produced with latch needles according to the invention.
According to an advantageous feature of the invention which contributes to the above-discussed highly satisfactory results, the inner contour of the latch has rounded lateral edges. Such rounded lateral edges are, by virtue of the narrow latch in grooved-hook-type latch needles, protected for a relatively long period from lateral abrasions and thus from developing sharp edges.
In accordance with another additional advantageous feature of the invention, in the grooved-hook-type latch needle the groove is shallow at least at the hook tip but preferably in its entirety to such an extent that at no location is it deeper than one-half of the hook thickness at that location. By virtue of this feature a weakening of the hook tip is avoided. Also, no sharp edges will form at the hook tip. Such a result is achieved despite the fact that by virtue of the stepped portion at the inner contour of the latch a smooth transition from the latch to the hook space is obtained.